Large discrepancies persist between projections of the physical impacts of climate change and economic damage estimates. These discrepancies increase with increasing global average temperature projections. Based on this observation, we recommend that in its Sixth Assessment Report (AR6), the Intergovernmental Panel on Climate Change (IPCC) improve its approach to the management of the uncertainties inherent in climate policy decisions. In particular, we suggest that the IPCC (1) strengthen its focus on applications of decision making under risk, uncertainty, and outright ambiguity and (2) estimate how the uncertainty itself affects its economic and financial cost estimates of climate damage and, ultimately, the optimal price for each ton of carbon dioxide released. Our hope is that by adopting these recommendations, AR6 will be able to resolve some of the documented inconsistencies in estimates of the physical and economic impacts of climate change and more effectively fulfill the IPCC’s mission to provide policymakers with a robust and rigorous approach for assessing the potential future risks of climate change.(my bold). Obviously, a "projection of physical impacts" and an "economic damage estimate" are two different things. For there to be a discrepancy you'd need, well, something obvious would be 10 m of SLR and very little economic damage. Obviously no paper making such a strong assertion would fail to support it, so let's go look.
In the Inconsistent Assessment of Risks in the IPCC Fifth Assessment Report (AR5) section they kinda make three arguments: (1) There is now a growing awareness of the limitations of the existing generation of IAMs; (2) these estimates largely ignore the potential for “tipping points”; and suggest (3) strengthening its focus on decision making under uncertainty and outright ambiguity. (1) isn't clearly supported by refs; (2) gets you the standard answer; and (3) isn't clear in what way that represents a discrepancy.
But never mind that, because the next section is called Evidence of Discrepancies Between Scientific and Economic Assessments of Climate Impacts; it's just bound to be in there. And the relevant text appears to be "DICE, for example, projects a loss of less than 10 percent of global economic output as a result of raising the global mean surface temperature by 6°C". But while that might be a discrepancy, it isn't obviously. And their reference for it is "Climate Shlock", a book wot one of 'em wrote. That's not a scholarly reference. And as apparently the key reference to their key point, it's just a little careless. They continue physical impacts are often not translated into monetary terms and they have largely been ignored by climate economists which is odd. The IAMs don't include everything, but to express it in this way is strange. Is this Pindyck again?
I don't think I'm trying to defend IAMs at this point. Just point out that this paper seems rather ill considered. A case for tighter refereeing I think.
* The rich want to live in the Anglosphere.
* What’s the damage (of that climate change cost-benefit model)? - ftalphaville